Swine Wastewater Treatment Using Submerged Biofilm SBR Process: Enhancement of Performance by Internal Circulation through Sand Filter

Pollutants removal from swine wastewater by a submerged biofilm sequencing batch reactor (BSBR) with internal circulation of liquor through a sand filter was studied. The variation of nutrient removal efficiencies with changes in volumetric circulation ratios and rates were determined. The reactor was operated under the following conditions: One cycle per day, hydraulic retention time of 15 days, average ${\text{NH}}_4–\text{N}$ loading rate of $55\text{g}{\text{m}}^{-3}{\text{d}}^{-1}$ , and without supplemental external carbon source. System performance was enhanced by conducting internal circulation of liquor through the sand filter. When compared with the performance of a single BSBR without sand filter, nitrogen and phosphorus removal efficiencies were found to increase by 18% and over 33%, respectively. With a circulation rate of $170\text{L}{\text{h}}^{-1}{\text{m}}^{-3}$ , and duration of 22 h (circulation ratio of 0.9), TOC, ${\text{NH}}_4–\text{N}$ , and total soluble inorganic nitrogen (as ${\text{NH}}_4–\text{N}$ plus ${\text{NO}}_x–\text{N}$ ) removal efficiencies of 73, 97.8, and 85.6%, respectively, were achieved. The enhancement of nitrogen removal was attributed to the occurrence of denitrification in the sand filter during circulation of liquor. The denitrification rate was proportional to the volumetric circulation ratio per day, resulting in an average 15% ${\text{NO}}_x–\text{N}$ removal in the sand filter. Also, it was found that continuous circulation during the entire reaction phases could be one way to achieve better performance.